Linux support

You can read/write large SDHC cards since Linux kernel version 2.6.22, this has been tested on X41 Tablet, X41 and X40 with 16 GB SDHC (FAT32), 4 GB (non-HC, FAT32) and 2 GB (non-HC, FAT16) cards. However there have been some old reports that you can't, delete, create, resize or format partitions, there seems to be no problems with this on 2.6.24. These problem will not exist if you use an USB connected SDHC card reader instead of the internal one, so you can always use the cards.

The driver was coded by the SDHCi project supporting these and other SD controller chips, making them work with SDHC cards as well. The driver (modules sdhci and sdhci_pci) has been reported to work on ThinkPad X40, X41, Z60m, Z60t, X60 and X61 models, and has been available in mainline kernel since 2.6.17-rc1. See also "How to get the internal SD card working".

Problems with Standby / Hibernate

Add the follwing line to the # /etc/pm/config.d/00sleep_module to unload the module before standby:

SUSPEND_MODULES="$SUSPEND_MODULES sdhci"

"Got data interrupt" error messages

If you see error messages like

mmc0: Got data interrupt 0x00200000 even though no data operation was in progress.

after inserting an SD card, try re-loading the sdhci module with a parameter debug_quirks=0x40. Solved the problem on a T61.

Windows support

The Microsoft hotfix 934428 is available here [1] it adds SDHC (SD High Capacity) support to Windows XP SP2 systems.

02-01-2009 NOTE for SDHC cards using Windows 2003 Server and Vista. IBM/Lenovo nor Microsoft supports this KB934428 with 2003 Server and the update.exe halts with OS version mis-match error when executed on 2003 or Vista despite the fact the sff*.sys driver files are perfectly compatible.
Manual extraction and installation of the driver file still fails to properly mount and read 4GB+ SD cards despite indicators and messages of successful installation.
Solution requires obtaining sdhcinst.dll from 2003 install media or copying from the %systemroot%\system32 directory into the %systemroot%\system32\drivers directory before manually installing driver files and pointing to the ..\SP2QFE\ic\sdbus.inf file. A copy of sdhcinst.dll copied from a KB934428 patched XP workstaiton is identical to all 2003 Server versions and Vista since Microsoft clings to a universal drivers model.
The KB934428 doesn't include the sdhcinst.dll file.
Follow this link to lenovo forums for longer but just as simple explanation.

[2]
[OT] This solution has also been successfully tested on systems from different manufacturers and with non Richo card readers.